Most of the time when it stinks and your eyes are watering the engine is lean as poop.

If all the circuits are working well besides the curb idle, it seems like it would be worthwhile to do some extra cleaning in that circuit. Fine stuff settles in low spots and odd corners and sometimes plug things up even after a typical cleaning and rebuild.

If it was my carb, I'd start with removing the air bleed screw and spraying in there, followed with some air if you have. While doing it, look to see if fluid is coming through the idle ports evenly. Because the air bleed feeds into the idle circuit, cleaning fluid should be coming out into the venturies.

Next, I'd remove the plugs for the idle fuel restrictions. According the MTSC booklet '68 Service Features' Carburator Clinic there are limiter screws underneath. Count the 1/8 turns in to seated, write down, and then remove. Spray in there and again make sure fluid is coming out each idle port. Reinstall limiters.

Again if it was me, I'd try it without resealing the limter screws. That way IF the air adjustment screw does not provide the desired range, the limiter screws can be played with. Its actually pretty cool that you can adjust the air bleed as well as the fuel restrictions with the turn of a screw driver. (easy for me to say, since I don't know how easy it is to get a screwdriver into those restrictors whe the carb is on the engine!) But heck if I had that carb, I'd be playing with it.

If you ever want to show as a restoration, you can put plugs back over the limiter screws.

Besides the shop manuals and the Service Features pamphlet, there is a an entire '68 MTSC pamplet 1968 Carburator Service Highlights at Imperial club org to check out.

either the throttle blades are too far open at idle and exposing the fuel transfer slot, or someone over tightened the idle screws at one time and made the idle holes way larger?

I'll bet there is a vaccum leak at the throttle shaft's. Spray carb cleaner around the throttle shafts with it idling fully warmed up and i bet the idle smooths out.

I still need to set timing exact but otherwise the carb isn't running all that bad. I'll probably leave it for now to save $$$. It's still a bit rough when cold but runs well once warmed up.